Process for the preparation of silver halide emulsions

ABSTRACT

The photographic properties such as sensitivity and graininess of silver halide emulsions can be improved by performing the precipitation of silver halide and/or the afterripening in presence of silicic acid sols instead of or in admixture to gelatin as protective colloid. The agglomeration of silicic acid particles which often occurs at high concentrations of salts can be avoided by addition of ethanol or of water-soluble polymers or by the preparation of such polymers in the silicic acid sol.

United States Patent Saleck et al.

[451 Jan. 25, 1972 PROCESS FOR THE PREPARATION OF SILVER HALIDE EMULSIONS Inventors: Wilhelm Saleck, Gladbach-Schildgen;

Wolfgang I-limmelmann, Opladen-Luetzenkirchen; Rudolf Meyer, Leverkusen; Franz Moll; Harald Huckstadt, both of Cologne, Stammheim, all of Germany Agfa-Gevaert Aktiengesellschaft, Leverkusen, Germany Filed: Sept. 2, 1969 Appl. No.: 854,792

Assignee:

Foreign Application Priority Data Sept. 5. 1968 Germany ..P 17 97 254.2

US. Cl ..96/94, 96/108, 96/114, 96/114.7

Int. Cl ..G03c 1/02 Field of Search ..96/94, 1 14.7, 108

References Cited UNITED STATES PATENTS 1/1953 Webster ..96/114.7 11/1954 Gray ..96/1l4.7

2,752,246 6/1956 Weaver ..96/1 14.7 3,411,907 11/1968 Whitmore et a1. ..96/94 FOREIGN PATENTS OR APPLICATIONS 1,267,931 3/1968 Germany OTHER PUBLICATIONS Photographic Chemistry, 1958, Glafkides, pp. 43 l 432. The Condensed Chemical Dictionary, Seventh Edition, Rose et aL, 1968, p. 843.

Primary Examiner-.l0hn T. Goolkasian Assistant ExaminerGeorge W. Moxon, ll At!0rneyConnolly and Hutz 57 ABSTRACT 9 Claims, No Drawings PROCESS FOR THE PREPARATION OF SILVER HALIDE EMULSIONS The invention relates to a process for the preparation of silver halide emulsions, in which process precipitation or afterripening is carried out in the presence of silicic acid sols which act as protective colloids.

The preparation of photographic silver halide emulsions comprises substantially three stages:

1. Precipitation of the silver halide in the presence of a protective colloid, generally gelatin, by reacting aqueous solutions of a silver salt, e.g., silver nitrate with aqueous solutions of alkali metal halides.

2. Solidification or flocculation followed by washing to remove the excess soluble alkali metal salts.

3. Redispersion with gelatin and afterripening by the addition of ripening substances or chemical sensitizers.

The substance which is mostly used as a protective colloid and binder for silver halide emulsions is gelatin. No other natural or synthetic binders have achieved any practical importance because it is only with gelatin that the necessary light sensitivity can be achieved.

The photographic properties of silver halide emulsions, e.g., their sensitivity to light the characteristic curve, fog formation, etc., can be altered as desired by the use of certain additives. These properties can also be influenced by modifying the method of preparation. The method of precipitation is of special importance for the graininess of the silver halide emul- SlOn.

Owing to the many different requirements which have to be met by photographic silver halide emulsions, further improvements, especially as regards sensitivity, stability to fogging, and fineness of grain are of great practical interest.

It is among the objects of the present invention to provide photographic silver halide emulsions which have improved photographic properties.

We now have found a process for making light-sensitive silver halide emulsions comprising the steps of precipitating the silver halide in the presence of a protective colloid, solidification or flocculation and washing of the emulsion followed by afterripening wherein precipitation of the silver halide and/or afterripening is performed in the presence of colloidal silicic acid sol.

Sensitivity increases of up to about 3 DIN, i.e., of a whole shutter stop, are easily achieved by the process according to the invention without any further alterations to the silver halide emulsion. In addition, fogging is considerably reduced. The emulsions prepared by the process according to the invention provide images which have substantially reduced graininess. The characteristic curve of these emulsions shows an extended rectilinear form which is extremely desirable for most photographic processes.

The usual silicic acid sols are suitable for the process according to the invention, regardless of whether the silicic acid has been prepared by a wet decomposition process or a pyrogenic process. The size of the colloidal silicic acid particles in the sol should be relatively small. Particle sizes of up to 100 p and preferably between 7 and 100 p. have been found to be generally suitable.

The symbol ,1. as used herein indicates millimicrons or nanometers.

Suitable results are also obtained with silicic acid sols containing up to 20 percent by weight of aluminum oxide related to the solid content.

The concentration of silicic acid in the silicic acid so] may vary within wide limits. The concentration and type of silicic acid sol which is suitable for any particular silver halide emulsion can be easily determined by a few simple tests.

Aqueous silicic acid sols in concentrations of 0.1 to 30 percent have proved to be suitable for the preparation of most silver halide emulsions. At high silicic acid concentrations, care must be taken to ensure that the silicic acid particles do not agglomerate to form larger particles which may impair the properties of the emulsion, e.g. due to the formation of a rough surface in the finished silver halide emulsion layer. Agglomeration can be easily avoided by adjusting suitably the concentration of alkali metal halide and silver salts during precipitation. If the concentrations of silicic acid are relatively high, relatively dilute salt solutions should be used for precipitation. 0.1 to 1 percent silicic acid sols have proved to be the most advantageous for the process of the invention.

Sometimes it is desirable to work at high concentrations of alkali metal salts and silver salts in which case often agglomeration of silicic acid particles occurs upon addition of silicic acid sols to the reaction mixture. This agglomeration, however, can easily be avoided by various measures.

Treatment of the silicic acid sols with ethanol (96 percent) before the addition to the reaction mixture has proved to be suitable. The amount of ethanol necessary for this purposes can vary within wide limits, for example between 20 and 100 ml. and preferably between 40 and 70 ml. per 100 ml. ofa 30 percent aqueous silicic acid sol. Sometimes it is also advisable to add the same amount of ethanol during the afterripenin g to avoid an agglomeration in this step of preparation of emulsion. The same applies also for the casting, especially if the casting solution has to stand for a longer time. Addition of a certain amount of ethanol in this case can be useful.

It has also proved useful to prevent the agglomeration of silicic acid particles by polymerizing in the silicic acid sols any monomers which are sufficiently soluble in water. Useful monomers are for example acrylic acid, methacrylic acid and derivatives thereof, such as acryl amide, acrylonitrile, methacryl amide or methacrylonitrile, or vinylsulfonic acid, or mixtures of the monomers mentioned before. The polymerization is started by addition of a radical forming compound such as potassium persulfate or azadiisobutyronitrile. After the polymerization step the reaction mixture is dialyzed to remove undesired byproducts and especially the remaining polymerization starter which otherwise would deleteriously affect the photographic properties of the emulsion.

Amounts of the monomers used for the polymerization which are between 0.5 and 20 percent by weight, and preferably between 0.5 and 2 percent by weight related to the solid content of the sols have proved to be useful. The polymerisate is used at least in such a concentration as to avoid agglomeration and at most in such a concentration as to attain improved photographic results, for example, higher sensitivity or finer graininess.

Nearly the same results can also be obtained by addition of a suitable amount of a polymer obtained by homoor copolymerization of the monomers mentioned above. For example, the agglomeration can be prevented by addition of polyacrylic acid, polyacryl amide, polyacrylonitrile or polyvinyl alcohol. Furthermore, the addition of gum arabic or polyvinyl pyrrolidone, for example, has been useful. The concentration which is suitable for any particular silver halide emulsion can be easily determined by a few simple tests. In principle these additives are used in the same concentration as the monomers mentioned above. The polymers added to or prepared by polymerization in the aqueous silicic acid sols must be sufficiently soluble in this medium.

The process of the invention is suitable for the preparation of silver chloride, silver bromide, silver iodide or mixed emulsions. The usual variations of the process can be easily used for precipitation. For example, the aqueous solutions of the silver salt and of the alkali metal halide may be run in simultaneously, but equally well one of the components for precipitation may be introduced first into the reaction vessel. Neutral emulsions or ammoniacal emulsions may equally well be prepared by the process according to the invention.

When precipitating the silver halide by the process according to the invention, the silicic acid sol may be used as the only protective colloid or in admixture with gelatin as a protective colloid. In the latter case, the proportion of gelatin to silicic acid may vary within wide limits. Proportions by weight of between 1:0.] and 0.0:l have been found to besuitable in most cases.

If precipitation is carried out with silicic acid sol as the only protective colloid, silicic acid sols which have previously been treated with anion exchangers or cation exchangers have proved to be particularly suitable. The pH of such silicic acids is 4 or less. For the precipitation of neutral emulsions, the pH may then be adjusted to the region of 5 to 7 without any ag glomeration of the silicic acid sol being observed.

Precipitation is performed preferably at a pH of between 6.0 and 7.0.

Gelatin in the usual quantities is advantageously used for redispersing the precipitated emulsion before chemical ripening. The concentration of the silicic acid sol is preferably such that up to 20 percent by weight and preferably up to 10 percent by weight of the total amount of binder in the finished emulsion consists of silicic acid.

The emulsions can also be optically sensitized with cyanine dyes such as basic or acid carbocyanines, cyanine dyes of the betaine type, rhodacyanine or merocyanine dyes, styryl or oxonol dyes. Suitable sensitizers are described by F. M. l-lamer The Cyanine Dyes and related Compounds lnterscience Publishers, 1964).

The emulsions may also contain chemical sensitizers, e.g., reducing agents such as stannous salts, polyamines such as diethyltriamine or aminomethane sulfinic acids or derivatives thereof such as described in Belgian patent specification No. 547,323 or sulfur compoundsas described in US. Pat. No. 1,574,944, for example allyl thiocyanate, allylthiourea, sodiumsulfate and the like. Suitable chemical sensitizers are also salts of noble metals such as ruthenium, rhodium, palladium, iridium, platinum or gold, as described in the article by R. Koslowsky, Z. wiss.phot. 46, 65-72 (1959). Further suitable 'for chemical sensitization are polyalkylene oxides, especially polyethylene oxide having an average molecular weight of l,000 to 20,000 and derivatives thereof, such as condensation products of alkylene oxides with aliphatic alcohols, glycols,

cyclic dehydration products of hexitoles, alkyl substituted 'phenols, aliphatic carboxylic acids, aliphatic amines, diamines or amides-The said condensation products have preferably a molecular weight of above 1,000. It is also possible to apply combinations of several chemical sensitizers.

Particular suitable for the emulsion of the present invention are chemical sensitizers of the thiomorpholine series such as described in French Pat. No. l,506,230.

The emulsions according to the invention may additionally contain the usual stabilizers, e.g., homopolar or salt-type compounds of mercury with aromatic or heterocyclic rings, such as mercaptotriazoles, simple mercury salts, sulfonium mercury double salts, and other mercury compounds. Other stabilizers which may be used include azaindenes, especially tetraor pentaazaindenes, in particular those substituted with hydroxyl or amino groups. Compounds of this type have been described in the article by Birr, Z.wiss.phot. 47, 258 (1952). Other suitable stabilizers include heterocyclic mercapto compounds, e.g., l-phenyl-5-mercapto-tetrazole, quaternary benzthiazole derivatives and benztriazoles.

The emulsions may be hardened in the usual manner, for example, with formaldehyde or halogen-substituted aldehydes that contain a carboxyl group, e.g., mucobromic acid, diketones, methanesulfonic acid esters and dialdehydes.

The emulsions prepared by the process according to the invention can be used for all sorts of different photographic material, e.g., for phototechnical films, for making printed copies or material for taking originals, especially highly sensitive material of this kind. They may also be used for X-ray films, for any type of color photographic material, e.g., material used for the silver dye bleaching process, and for photographic material intended for use in the silver salt diffusion process or any other instant image-forming process.

EXAMPLE 1 Emulsion] Thirty ml. of a 30 percent aqueous colloidal solution of silicic acid (pH 8.3; particle size about l4 ,4; stabilized with NaOH) are added to a solution of 78 g. of ammonium bromide, 7.2 g. of potassium iodide and 10 g. of gelatin in 1 liter of water. The reaction mixture is adjusted to a pH of 6.8 and heated to 65 C.- A solution of g. of silver nitrate in 1,200 ml. of water, which is at about the same temperature as the solution in the reaction vessel, is then run in the course of 40 minutes. The resulting emulsion is cooled to 30 C. and flocculated by the addition of a concentrated solution of ammonium sulfate.

The fiocculate is given time to settle, decanted and washed several times with water. The washed flocculate is taken up in a solution of g. of gelatin in 1,200 ml. of water. The pH is then adjusted to about 6.6, the pAg to 8.9 and the viscosity to about 10 cp.

Chemical ripening to maximum sensitivity is then carried out in the usual manner at about 50 C. after the addition of the usual sulfur compounds and gold salts. Emulsion ll The emulsion is prepared in the same way as emulsion l but without the addition of silicic acid sol.

Emulsion Ill The emulsion is prepared in the same way as emulsion II but 30 ml. of the silicic acid sol described for emulsion l are added before chemical ripening.

Emulsion IV The emulsion is prepared in the same way as emulsion ll. Thirty ml. of the silicic acid sol are added after chemical ripening.

The emulsions are then then processed in identical manner. Ten ml. of a 10 percent aqueous formaldehyde solution as hardener, l2 ml. of a 7.5 percent aqueous saponin solution as wetting agent and 20 ml. of a 1 percent methanolic solution of 4-hydroxy-6-methyl-l,3,3a,7-tetraazaindene as stabilizer are added. The finished casting solutions are applied onto a support of cellulose triacetate.

The layers are exposed in a conventional sensitometer through a step wedge. The exposed samples are developed in a bath of the following composition for 6 minutes, and in a second parallel test for 16 minutes:

Sodium sulfite, anhydrous 70.0 g. Borax 7.0 g. Hydroquinone 3.5 g. p-monomethylaminophenol 3.5 g. Sodium citrate 7.0 g. Potassium bromide 0.4 g.

made up to l liter with water.

The layers are then fixed with a sodium thiosulfate solution. The results of the sensitometric tests are summarized in table I below.

for precipitation.

These samples are processed as described in example i. The different types of silicic acid sol added to the emulsions had the following properties:

Emulsion V Thirty percent silicic acid sol stabilized with NaOI-I, pH 8.3, particle size about 14 ,u. Emulsion VI Fifteen percent, particle size 7 to 9 u. Emulsion VII Thirty percent, mixed with A1 sol, pH 9.1, particle size 14 to 15 u. Emulsion VIII Thirty percent, stabilized with NaOI-I, pH 9.9, particle size 14 to 15 ,l. Emulsion IX Thirty percent, stabilized with NaOI-I, pH 9, particle size 5 IO [.L. Emulsion X Fifteen percent, dispersion of finely divided SiO prepared pyrogenically, particle size to p" Emulsion XI Twenty-eight aqueous dispersion of pyrogenically prepared SiO particle size about 15 u.

The results of the sensitometric test are given in table 11 below:

Emulsion XII The emulsion is prepared in the same way as emulsion I of example I, but with a silicic acid sol of the same particle size which had been treated with anionic and cationic exchangers. The silicic acid sol has a pH of 3.4. Before it is used as protective colloid in the precipitation, it is adjusted to a pH of 6.8. Emulsion XIII The emulsion is prepared in the same way as emulsion I, but precipitation is carried out only in the presence of the silicic acid sol described above, without gelatin. After precipitation, a solution of 10 g. of gelatin in 100 ml. of water is added to enable flocculation to take place.

The emulsion is processed as described in example 1. The results of the sensitometric test are given in table 111 below. The comparison emulsion given in the table was prepared in the same way but without the addition of silicic acid sol.

Table III 16 min. 6 min. development time development time Scnsi Sensitivity l 7 Fog tivity y Fog Comparison emulsion standard 0.45 0.12 standard 0.65 0.16 Emulsion XII +2.0 0.40 0.06 +2.0" 0.60 0.10 Emulsion XIII +1.5 0.40 0.08 +1.5 0.55 0.12

EXAMPLE 4 Emulsion XIV The emulsion is substantially the same as emulsion I of example I. Emulsion XV The emulsion is prepared like emulsion XIV, but 2 ml. of a 1 percent aqueous solution of 6-azonia-9-sulphaspiro-5,5-undecane chloride according to French Patent Specification 1,506,230 are added to the precipitation component.

The emulsion is processed as described in example I. The results of the sensitometric test are shown in table IV below.

Thirty ml. of a 30 percent aqueous colloidal solution of silicic acid (pH 8.3; particle size about 14 ,u.; stabilized with NaOI-I) are added to a solution of g. of ammonium bromide, 7 g. ofpotassium iodide and 10 g. of gelatin in 800 ml. of water. The reaction mixture is adjusted to a pH of 6.8 and heated to 65 C. A solution of 120 g. of silver nitrate in 1,000 m1. of water, which is at about the same temperature as the solution in the reaction vessel, is then run in the course of 40 minutes.

The resulting emulsion is further treated in the same way as described for emulsion 1 (example 1).

Emulsion XVII The emulsion is prepared in the same way as emulsion XVI but the silicic acid solis treated with 20 ml. of ethanol (96 percent) before addition to the reaction mixture. Also the same amount of ethanol is added to the emulsion before afterripenmg.

Emulsions XVIII-XXVII In the preparation of these emulsions is added a silicic acid so] as described for emulsion XVI but in the silicic acid sol have been polymerized before addition various monomers in various amounts given in the table V. After polymerization the solution is dialyzed. For example, the silicic acid sol for the preparation of emulsion XIX has been prepared as follows:

To 100 ml. ofa 30 percent aqueous colloidal solution of silicic acid (pl-I 9,1; particle size 14-15 11.; surface l95-2l5 mF/g.) are added 3.0 g. sodium acrylate and 0.1 g. potassium persulfate. The mixture is heated for minutes up to 60-70 C. After this polymerization step the reaction mixture is dialyzed 48 hours whereupon the concentration is determined.

Table V Additive Amount Emulsion (to be polymerized) (percent by weight) XVIII acrylic acid 20 XIX acrylic acid 10 XX acrylic acid 4 XXI acrylonitrile 5 XXII acrylonitrile l X XIII acrylonitrile 0,5 XXIV acrylamide 2 XXV acrylamide 5 XXVI acrylamide 10 XXVII vinylsulfonic acid 2 Emulsions XXVIILXXXII ln the preparation of these emulsions is added a silicic acid sol as described for emulsion XVI but the silicic acid sol has been mixed thoroughly with one of the additives given in table Vl.

All emulsions are casted upon a support, dried, exposed, and processed as described in example 1. The agglomeration of silicic acid particles can be tested optically by means of a microscope with a magnification of at least 200, or by examining the roughness of the processed and dried film with the finger. Agglomeration occurs in emulsion XVI. But no agglomeration can be found in emulsions XVII through XXXll.

We claim:

1. In a process for making light-sensitive silver halide emulsions comprising the steps of precipitating the silver halide in the presence of a protective colloid, obtaining a suspension to produce an emulsion, washing the emulsion and chemical ripening the improvement consisting of precipitating the silver halide in the presence of colloidal silicic acid sol having a particle size of between and 50 am, said silicic acid sol being a protective colloid.

2. The process of claim 4, wherein precipitation of the silver halide is performed in the presence of gelatin as additional protective colloid.

3. The process of claim 1, wherein the precipitation is performed in the presence of silicic acid sols which have been treated with an ion exchanger.

4. The process of claim 1, wherein the silicic acid sols contain between 0.1 and 1 percent of silicic acid.

5. The process of claim 1, wherein the silicic acid sols contains up to 20 percent by weight of aluminum oxide, related to the solid content.

6. The process of claim 1, wherein the silicic acid sol contains 10-50 percent by volume of ethanol.

7. The process of claim 1, wherein the silicic acid sol contains in dissolved form 05-20 percent by weight related to the solid content of gum arabic, polyvinyl alcohol, polyvinyl-pyrrolidone or of a homoor copolymerisate of acrylic acid or of derivatives thereof.

8. The process of claim 7, wherein the homoor copolymerisate has been prepared in the silicic acid sol by polymerization of at least one monomer selected of the group consisting of acrylic acid, derivatives of acrylic acid and vinylsulfonic acid.

9. In a process for making light-sensitive silver halide em ulsions comprising the steps of precipitating the silver halide in the presence of a protective colloid, obtaining a suspension to produce an emulsion, washing the emulsion and chemical ripening the improvement consisting of chemical ripening the emulsion in the presence of colloidal silicic acid sol having a particle size of between S and 50 nm., said silicic acid s'ol being a protective colloid. 

2. The process of claim
 1. wherein precipitation of the silver halide is performed in the presence of gelatin as additional protective colloid.
 3. The process of claim 1, wherein the precipitation is performed in the presence of silicic acid sols which have been treated with an ion exchanger.
 4. The process of claim 1, wherein the silicic acid sols contain between 0.1 and 1 percent of silicic acid.
 5. The process of claim 1, wherein the silicic acid sols contains up to 20 percent by weight of aluminum oxide, related to the solid content.
 6. The process of claim 1, wherein the silicic acid sol contains 10-50 percent by volume of ethanol.
 7. The process of claim 1, wherein the silicic acid sol contains in dissolved form 0.5- 20 percent by weight related to the solid content of gum arabic, polyvinyl alcohol, polyvinyl-pyrrolidone or of a homo- or copolymerisate of acrylic acid or of derivatives thereof.
 8. The process of claim 7, wherein the homo- or copolymerisate has been prepared in the silicic acid sol by polymerization of at least one monomer selected of the group consisting of acrylic acid, derivatives of acrylic acid and vinylsulfonic acid.
 9. In a process for making light-sensitive silver halide emulsions comprising the steps of precipitating the silver halide in the presence of a protective colloid, obtaining a suspension to produce an emulsion, washing the emulsion and chemical ripening the improvement consisting of chemical ripening the emulsion in the presence of colloidal silicic acid sol having a particle size of between 5 and 50 nm., said silicic acid sol being a protective colloid. 